The increasingly tense stand-off between the U.S. and North Korea may have hit a new high this week. As U.S. and South Korean military units conducted an annual air power exercise over the Korean Peninsula, China’s air force reportedly staged exercises in “routes and areas it has never flown before” over the Yellow and East Seas. The exercise involved reconnaissance planes, fighter jets, an early warning and control aircraft, and a joint operation with surface-to-air missile units.

The South China Morning Post quotes Li Jie, a Beijing-based military expert, as saying the drills were done specifically to send a message to Donald Trump. “The timing of this high-profile announcement by the [People’s Liberation Army] is also a warning to Washington and Seoul not to provoke Pyongyang any further,” Jie told the Post. The U.S. and South Korea used over 200 aircraft in their recent drills. North Korea has protested the exercise as an “all out provocation.”

Whether Jie is correct about the intentions of the Chinese air force is tricky to determine at this point. China has previously condemned North Korea for launching test missiles and, three months ago, backed U.N. sanctions against the country after a significant nuclear test.

Trump’s view of how China has reacted to North Korea’s actions, as judged by his tweets, has run the gamut. In early November, he wrote “My meetings with President Xi Jinping were very productive on both trade and the subject of North Korea. He is a highly respected and powerful representative of his people.” He praised the country for sending an envoy to speak with the North Korean government, but seemed frustrated earlier this month by the lack of results from that meeting.